(1) Field of the Invention
The present invention relates to molded polymeric structural members and compositions and methods for making them.
(2) Description of the Related Art
Wooden building structures, such as door frames and window frames, may be prone to deteriorate when exposed to environmental weathering. For example, once water contacts a wooden door frame, it can wick along the wood to be absorbed throughout the frame. To counteract such weathering, it is desirable to construct door frames of clear lumber that is moisture-resistant, free of knots, and capable of being stained and/or painted to give high quality results. Unfortunately, such high quality lumber has become more difficult to obtain and costly.
Further, there can be significant waste involved in manufacturing wooden door frames and window frames. Typically, frames for windows and doors are made of separate parts that are then assembled to form the frame. For example, door frames generally include two vertically spaced jambs that define the sides of the frame, and a header (or head jamb) that defines the top of the frame. In some cases, the frame also includes a threshold or sill that defines the bottom of the frame. To manufacture a door frame, a tree must be debarked, the limbs removed, and the truck cut into elongate strips of lumber. Next, knots and other irregularities are removed and the remaining pieces of wood are finger-jointed together. At this point, the lumber is typically an elongate strip that is essentially free of knots and other irregularities. The lumber is then molded and shaped to the final configuration required, and the jamb assembled. After priming, weather stripping may be secured to the jambs, and the frame, including two side jambs, a header jamb and optionally, a bottom sill, is assembled. Even with highly efficient manufacturing protocols, the process may result in large amounts of the original wood being wasted or relegated for other manufacturing purposes.
Also, as window and door frames are exposed, there is a tendency for the frame to be bumped by objects being transported through the window or doorway. Thus, the frame should be resistant to scratching or chipping upon impact. While frames made of high quality lumber are aesthetically pleasing, real wood may not be particularly resistant to physical impact.
Some attempts to reduce reliance on wooden door and window frames have included the use of plastic or vinyl clad wooden frame members (see, e.g., U.S. Pat. Nos. 5,987,843, 6,295,779, and 6,378,266). Still, these types of frames may be less aesthetically pleasing to many consumers and may require time-consuming manufacturing steps such as milling the wooden jambs, extruding the vinyl cladding to the appropriate shape, and fitting the cladding on the jamb. Alternatively, door frames that are entirely synthetic have been developed. Plastic frame members are attractive from a manufacturing standpoint in that they can be molded to provide a desired shape, and can accommodate attachment fixtures without the use of nails, screws or other types of fasteners (see e.g., U.S. Pat. No. 6,393,779). In some cases, however, plastic door jambs do not provide the support required to hold a door, and can buckle under extreme temperature conditions. To provide increased strength, the polymers used for the frame part may be combined with wood fiber, glass fiber, or other types of reinforcing material (see e.g., U.S. Pat. Nos. 6,412,227, 6,531,010, and 6,680,090). Alternatively, larger reinforcing members may be placed at strategic points within the frame part to stabilize the frame member and allow for attachment of other parts (see e.g., U.S. Pat. No. 6,453,631).
Metal door frames, or door frames having metal cladding, have been developed (see e.g., U.S. Pat. No. 6,604,334). Still, metal cladding may not be as aesthetically pleasing to some consumers. Also, metal frames typically suffer from substantial energy loss upon exposure to very hot or cold temperatures, and can suffer from environmentally induced weathering such as rust and photochemical deterioration.
Thus, there is a need to manufacture building parts, such as window frames and door frames, that have increased strength and that do not require the use of expensive, high quality lumber. There is also a need to develop door frames and window frames that are as aesthetically pleasing as wooden frames to the discerning consumer.